A water-cooled fuel cell system and an air-cooled fuel cell system are known as fuel cell systems mounted on fuel cell vehicles. In the water-cooled fuel cell system, heat generated by a fuel cell stack is cooled by cooling water. On the other hand, in the air-cooled fuel cell system, a fuel cell stack is cooled by cooling air supplied by a blower fan for cooling.
First, FIG. 4 shows the configuration of a general water-cooled fuel cell system of a conventional fuel cell vehicle. As shown in FIG. 4, in a water-cooled fuel cell system 101, a high-pressure compressed hydrogen gas stored in a hydrogen tank 102 is introduced into an anode intake portion 106 of a fuel cell stack 105 via a decompression valve 104 by using a hydrogen supply pipe 103.
Moreover, in the fuel cell system 101, the outside air sucked into an intake duct 107 is cleaned by a filter 108, thereafter compressed by a compressor 109, and then introduced into a cathode intake portion 110 of the fuel cell stack 105. As a result, in the fuel cell stack 105, electric power is generated by electrochemical reaction between hydrogen and oxygen in the air.
Excess air is discharged from a cathode exhaust portion 111 of the fuel cell stack 105 to an exhaust duct 112 as cathode exhaust. After part of moisture in the cathode exhaust is separated by a steam separator 113, the cathode exhaust is introduced into an exhaust duct 112 through a back pressure valve 114 intended to control the pressure of a code system and is released to the outside of the vehicle.
Moreover, an excess hydrogen gas is discharged from an anode exhaust portion 115 of the fuel cell stack 105 as anode exhaust. The anode exhaust also passes through a steam separator 116 like the cathode exhaust, is introduced into the exhaust duct 112 through a purge valve 117, and is mixed with the cathode exhaust. The flow amount of the anode exhaust is far smaller than that of the cathode exhaust. Accordingly, purged hydrogen in the anode exhaust can be diluted with the cathode exhaust to a concentration not higher than 4% which is the lower flammability limit, and then released to the outside of the vehicle. Depending on the type of the fuel cell system 101, the anode exhaust is recirculated to the anode intake portion 106 by using a hydrogen pump 118 to improve the utilization ratio of hydrogen.
The water-cooled fuel cell system 101 includes a cooling system 118. The cooling system 118 includes a loop-shaped cooling water passage 120 connecting the fuel cell stack 105 and a radiator 119 to each other, and circulates the cooling water between the radiator 119 and the fuel cell stack 105 with a water pump 121 to cool the fuel cell stack 105. The fuel cell system 101 utilizes high-temperature cooling water flowing through the cooling water passage 120 in a heating device 122. The heating device 122 supplies the cooling water to a heater core 124 by using an adjusting valve 123, drives a fan 125 for sending air, and thereby heats a vehicle cabin 3.
Next, the configuration of the air-cooled fuel cell system of a fuel cell vehicle is described by using FIG. 5. As shown in FIG. 5, also in an air-cooled fuel cell system 201, a compressed hydrogen gas stored in a hydrogen tank 202 is sent to a decompression valve 204 by using a hydrogen supply pipe 203 to be decompressed, and thereafter introduced into an anode intake portion 206 of a fuel cell stack 205.
On the other hand, a supply device of cathode intake has no high-pressure compressor. The supply device cleans air sucked into an intake duct 207 by using a filter 208 and then supplies the air to a cathode intake portion 210 of the fuel cell stack 205 by using a low-pressure blower fan 209. Air supplied to the cathode intake portion 210 not only is used for electric power generation reaction in the fuel cell stack 205 but also has a role of removing heat generated in the fuel cell stack 205 and cooling the fuel cell stack 205.
Cathode exhaust which is excess air discharged from a cathode exhaust portion 211 of the fuel cell stack 205 is released to the outside of the vehicle by using an exhaust duct 212. Moreover, anode exhaust which is an excess hydrogen gas discharged from an anode exhaust portion 213 of the fuel cell stack 205 passes through a purge valve 214 and is mixed with the cathode exhaust flowing through the exhaust duct 212. A purged hydrogen gas from the anode exhaust portion 213 is diluted with the cathode exhaust to a concentration not higher than the lower flammability limit, and then released to the outside of the vehicle.
Conventional heating devices of vehicles equipped with fuel cell stacks include the following heating devices. In one heating device (Japanese Patent Laid-Open No. 2008-108538), air discharged from a fuel cell stack is directly introduced into a vehicle cabin. In another heating device (Japanese Patent Laid-Open No. 2005-280639), a heat exchanger through which cooling water heated by heat generated in a fuel cell stack flows is disposed on a lower surface of a floor and an inside of a vehicle cabin is heated by utilizing the heat of the cooling water.